Videos from Mike AG5VG -- His Homebrew BITX Rigs

Here are two great videos from Mike AG5VG showing his two homebrew receivers in action.  (The transmitter portions of Farhan's circuit will come later.) See yesterday's post for more details. 

On the video above (40 meters) 

-- I love that speaker.  

--  The enclosure and the reduction drive for the VFO is really great.  FB OM. 

-- Very cool that Mike captures a 40 meter QSO with "Wild Bill" ZS6CCY in South Africa, someone who we've spoken to many times, often on the long path, sometimes from Mozambique. 

-- I like how Mike demonstrates the effect of removing the antenna.  You can definitely see what we mean when we say you should be able to "hear the band noise."   

  

Above you see the 20 meter receiver in action.  You can see one of the physical benefits of using a wooden base:  You can easily mount connectors, switches and tuning controls using just pieces of copper-clad board screwed into the wood.   This is what I am doing with my latest BITX 15-10 rig. 

For the tuning of the VFO, it looks to me as if Mike has a large "main tuning" control in the center, with a smaller "fine tuning" or "bandspread" control off to the left.  Does that smaller control work with a varactor diode or with a smaller variable cap?  Also, to the right of the main tuning control we see a 3 pole switch.  Is that switch putting additional L or C into the VFO circuit to move the frequency around?  These techniques would all be quite valid;  Mike demonstrates that there are many ways to skin a cat (or tune a VFO!) 

Mike:  Please send more info. 

Pine Boards, Analog VFOs, and Homebrew BITX Transceivers -- AG5VG's Magnificent Creations

Click in image for a better view

This is amazingly cool.  WE ARE NOT ALONE!  There are others out there breaking the tyranny of the Si5351, building BITXs with analog LC VFOs.  And using copper clad boards affixed to pine boards. Plywood cabinetry!  And medicine bottle coil forms.  Really great.  And what a wonderful workshop. Thanks Michael.     

Good Afternoon Bill,

This is Michael Sahn, AG5VG.

I hope your doing well, all is well here in south Texas. I have recently built a bitx20 receiver and bitx20 for 40 meters receiver.

I built it using the analog VFO and both of mine are stable. What an awesome feeling it is to have a stable homebrew VFO. I have attached pictures .

It’s been a fun journey to get to this step. I have just been enjoying the receiver as Farhan instructed us. Then I’m going to go through the transmit side.

Air core coils are great for VFO. On my bitx40 I used a medicine bottle bottom but I put the VFO in a tin can as you will see in the pictures.

The bitx20 is all out, hand capacitance is a slight issue but it’s all learning experience.

Going to be adjusting the pvc coil bandpass filter inductors, I think the value is a bit off so it’s not as loud as it should be, but everything else is set good.

Just wanted to check in and great job on the videos and podcasts. I really enjoy them

73s

Michael

Click on image for a better view

Click on image for a better view

Listen to Rex. W1REX. Lots of Tribal Wisdom in this Ham Radio Workbench Interview

 

https://workbench.libsyn.com/hrwb-193-building-projects-with-rex-harper-w1rex

This week's Ham Radio Workbench podcast features an interview with Homebrew Hero Rex Harper, W1REX of QRPMe fame. (The bulk of Rex's portion starts at about 1:26:30.)

I really liked this talk with Rex.  His enthusiasm for homebrewing is really inspiring -- it is very reassuring to know that there are others like us. Rex clearly has The Knack.  

I got a kick out of Rex's story about the outhouse at Dayton.  FB OM.  

Here is the video of the mojo transfer ceremony in which shared some of the Tuna Tin 2's mojo with my BITX 17.  Thanks again Rex!  

And thanks to George and the gang out at Ham Radio Workbench. 

Nine Homebrew Transceivers by Walter KA4KXX (and some QRP and QRO RC planes)

 

Our friend Walter KA4KXX in Orlando recently sent us this really cool "family photo" of his homebrew rigs.  Be sure to see the key that explains the photo (below) FB Walter.  Thanks too for the model airplane pictures. (Click on the images for better viewing.) 

Walter wrote: 

I recently realized that I am now operating nine homebrew transceivers, which would fit nicely in an “aerial” photograph, so I grabbed my stepladder and everything did fit well in the frame.  Six of them come from the BITX side of the family, with #1 and #7 direct conversion and #9 a single conversion superhet but using the NE602.  More basic information is included in the sketch.

I tried a Si5351 VFO once in the dual-band rig #4, but by the time I built the QRP Labs kit with so much closely-spaced soldering, and then added sufficient filtering and amplification to properly drive a 50 ohm load, I was exhausted!

These nine were created during the past eight years, and were preceded by eight more transceivers that I can document, but those have all been disassembled, with many of the parts being used in these later rigs.  I build my transceivers to be operated often, and since 20 Meters has been hot lately, for example, my POTA Hunter log shows over 300 CW and SSB contacts in 2023 alone, so rig numbers 7 - 9 have been earning their keep lately.

In summary I have created a lifetime total of seventeen transceivers so far, and although I am nowhere near the fifty-plus tally of Pete N6QW, I did spend a lot of years instead homebrewing many radio-controlled model airplanes of my own design.  Two photos show one example that I flew in the 2011 Blue Max Scale R/C Contest at the Fantasy of Flight Museum in Polk City, Florida against some stiff QRO competition.

—Walter KA4KXX

Farhan Describes his New 2 Meter SSB Transceiver (Video)

On May 16, 2023 Farhan gave us a look at his new BITX23 2 Meter Transceiver. Two days later he made a presentation on this rig at the Four Days in May event. Highlights: -- Use (and non-use) of the Cascade tool -- Cascade and the original BITXs -- ADE-1 -- SI570 -- Raspberry Pico -- Diplexer -- Different Grounds to get rid of digital noise -- Gimmick Capacitors (and gimmicks made from coax) -- Ugly SMD Capacitor Soldering -- Tombstoning! -- Melting RG-174 Coax -- No need to learn Arduino programming -- Dilbert! -- Bill and Pete -- Techie Tatts! Thanks Farhan!

Two days later, Farhan presenting the rig at FDIM

SolderSmoke Podcast #241 Mars, Direct Conversion, PTOs and Glue Sticks, Anniversary of the BITX20, Multus Proficio SDR, Boatanchor Station, MAILBAG

The board I use to test DC RX circuits 

SolderSmoke Podcast #241 is available

Audio (podcast):  http://soldersmoke.com/soldersmoke241.mp3

Video (YouTube): (215) SolderSmoke Podcast #241 October 28, 2022 - YouTube

Introduction:

Back on Mars.  Opposition approaching.  I have a Mars filter.  And (like T.O.M.) a Mars globe. 

N2CQR DXCC done

SolderSmoke in the WayBack Machine

Sticker news

PARTS CANDY -- Don't Scrimp with a Crimp! 

Bill's Bench

School DC RX projects -- in Hyderabad and Northern Virginia. 

Direct Conversion Receivers -- Keeping it Simple, Learning a Lot.  A step beyond the Michigan Mighty Mite. Do we really need 100db?  Do we really need to shield VFOs?  Farhan's super-simple and stable Colpitts PTO.  Audio amps, 1000-8 transformers and rolling your own LM386

PTOs and Glue Stick PTOs.  Paul Clark WA1MAC. Brass vs. Steel bolts.  #20 thread vs. #28 thread.  Backlash Blues. The best Glue Sticks. 

2 meters and the VWS.  Bill has a Baofeng. 

SHAMELESS COMMERCE:  MOSTLY DIY RF

Pete's Bench

20th Anniversary of the BITX20   Pete's early BITX rigs. 

Computer Woes

The Multus Proficio SDR rig

Simple SSB in China  BA7LNN

Things of beauty: Tempo One, NCX-3 and a SBE-33

MAILBAG

-- NS7V is listening.

-- Graham G3MFJ sent SPRAT on a stick.

-- Nick M0NTV  FB Glue Stick and 17 Shelf videos.

-- Dino KL0S HP8640 Junior

-- Mark AA7TA   Read the SolderSmoke Book

-- Steve EI5DD Connaught (Ireland) Regional News

-- Dave K8WPE  Planting the seeds of ham radio interest

-- Peter VK3YE Ruler idea on PTO frequency readout

-- Michael AG5VG Glue Stick PTO

-- Tobias  A polymath with UK and Italy connections.  And cool tattoos.

-- Alain F4EIT   French DC receiver

-- Michael S.  was in USMC, working on PCM/TDM gear

-- Alan Yates writes up Amazon transformer problem

-- Todd VE7BPO,  Dale W4OP, Wes W7ZOI

-- Farhan VU2ESE sent me an sBITX

-- Todd K7TFC   The Revenge of Analog

-- Jim Olds    Building QRP HB gear  

The Multus SDR rig Pete discussed

The older rigs Pete mentioned

My version of DC RX that Farhan is working on

My PTO with VK3YE's ruler frequency readout

SolderSmoke Podcast #156 -- November 4, 2013 -- Interview with Peter Parker VK3YE of Melbourne, Australia

November 4, 2013
Special hour-long interview with Peter Parker, VK3YE
-- Early experiences with radio
-- CW
-- DSB Gear
-- Simple gear, and gear that is TOO simple
-- VXOs, Super VXOs and Ceramic Resonators
-- Building receivers
-- Chips vs. Discrete
-- Making the leap to SSB
-- The Knob-less wonder and the BITX
-- No need for a sophisticated workshop
-- Advice for new phone QRPers

Peter's Blog: https://vk3ye.com/

Peter's YouTube Channel:  https://www.youtube.com/user/vk3ye/featured

Vienna Wireless Winterfest Hamfest 2022

After a two-year pandemic hiatus, yesterday the Vienna (Virginia) Wireless Society's annual "Winterfest" hamfest was back.  And the weather was in fact COLD -- it definitely felt like Winterfests of years-gone-by. 

Club President Dean KK4DAS kindly invited me to participate in a forum on homebrewing.  You can watch the presentation STARTING AT 2:04:06 (hours:minute:seconds) here: 

https://www.youtube.com/watch?v=s48of3uS9tM

It was especially cool to be able to tell the audience about Pete N6QW and Farhan VU2ESE. We talked about Pete's Simple SSB transceiver, the Michigan Mighty Mite and the BITX rigs. 

Some observations on the hamfest scene: 

-- There are lots of boatanchor radios out there, and it seems like a buyer's market.  These old rigs do not seem to be selling nearly as fast as they did a few years ago. 

-- There is a lot of older analog test gear on sale too, and it too seems to no longer be as in demand as it was a few years ago.  Perhaps the availability of cheap, small, and very effective digital oscilloscopes is affecting the sale of these once sought-after items. 

My purchases: 

-- A really old beat-up (crashed?) ARC-5 R-23 receiver.  I have already extracted the variable capacitor. 

-- A nice box of smaller variable caps. 

-- 100 feet of 550 parachute cord. 

-- Two nice metal chassis/boxes 

-- A bag of shaft adapters/connectors

With Armand WA1UQO (left) and Steve Boles W4SB (center)

With Charles AI4OT 

Thanks to Dean KK4DAS and the entire VWS team for a great event. 

Exorcism Completed! Getting Rid of the Spur in my 17 meter SSB Transmitter using a TinySA (video)

To re-cap:  The problem became evident when trying to "net" or "spot" my transmitter onto my receive frequency.  Around 18.116 MHz, I could hear at least two tones in the receiver as I moved the transmitter frequency.  I needed to get rid of the extra tone. 

First, thanks to all who sent in suggestions.  They came in literally from around the world, and this is a demonstration of the IBEW in action.  I used or at least tried all of them.  They were all good ideas. 

Following Vasily Ivananeko's pseudonymous suggestion I rebuilt the carrier oscillator (apologies to G3YCC).  I used the carrier oscillator/buffer circuit from Farhan's BITX20.   

Henk PA0EME said I should look at the signal level at the input ports of the NE602 mixer.  Henk was right --- the VXO input was far too high.  I lowered it, but the problem persisted. 

At first, I thought that the spur in question was so small that it would not show up on the air.  I could not see it in the TX output using my TinySA spectrum analyzer.  That was good news and bad news:  Good that it was not showing up on the air, bad that I could not see it in the TinySA and use that image in the exorcism. 

At first I thought that the spur was being caused by the 10th harmonic of the carrier oscillator and the third harmonic of the VXO.  This seemed to fit.  So, following VK3YE's sage advice, I built a little 69 MHz series LC trap (using a coil sent by AA1TJ, on a board CNC'd by Pete N6QW).  That trap succeeded spectacularly in crushing the 10 harmonic.  Look at these before and after shots on the TinySA: 

Before Trap

After Trap

Spectacular right? But guess what?  The problem was still there.  

I scrutinized the situation once more. I realized that the spur would be more visible if I put the TinySA on the input of the transmitter's PA (a JBOT amp designed by Farhan) as opposed to putting it on the output.  Watching the spur and the needed signal move in the TinySA as I tuned the VXO, I realized that they were moving in opposite directions.  This indicated that the spur was the result of a carrier oscillator harmonic MINUS a VXO-generated frequency (as the VXO frequency increased, the spur frequency decreased).  Looking at my EXCEL spread sheet, I could see it:  8th harmonic of the carrier oscillator MINUS the main output of the VXO. 

To confirm this, I plugged the values into W7ZOI's Spurtune program.  Yes, the spur popped up and  moved as predicted.  

For further confirmation I shut down the carrier oscillator by pulling the crystal from the socket, and then just clipped in a 5.176 MHz signal from my HP-8640B signal generator (thanks KB3SII and W2DAB). Boom!  On the TinySA, the spur disappeared.  Now I at least knew what the problem was:  a harmonic from the carrier oscillator.  

Following good troubleshooting practice, I turned off the gear and went to bed.  When I woke up, an idea came to me:  Before launching into a lot of filtering and shielding, just try running the carrier oscillator at a lower voltage, seeing if doing so might reduce the harmonic output.   I disconnected the carrier oscillator board from the main supply and clipped in a variable voltage bench supply.   Watching the signal on my TinySA, I watched as the spur completely disappeared as I reduced the voltage from around 13V to 10V  (see video above).  The main signal frequency level did not change much.  I tested this by listening for the hated extra tones.  They were gone.  Exorcised.  

Key lessons: 

-- Spur problems are difficult to troubleshoot.  Armstrong's superhet architecture is, of course, great, but this is definitely one of the pitfalls.  Single conversion makes life easier.  IF selection is very important. Choose wisely! 

-- When looking at the TinySA as you tune the rig, pay attention to which way the spur is moving.  This provides an important clue regarding the combination of harmonic you are dealing with. 

-- The TinySA is a very useful tool.  It seems like it is easier to use than the NanoVNA (which is also a fantastic tool). 

-- It can be fun and rewarding to re-visit old projects.  In the years between original construction and the re-look, new test gear has become available, and the skill and experience of the builder has improved.  So problems that once seemed insurmountable become fix-able. 

-- Thinking through a problem and thinking about possible solutions is very important.  It pays to step away from the bench to think and rest.  Rome wasn't built in a day. Here's a rough block diagram that I drew up (noodled!) while trying to figure out this problem: 

Farhan's Amazing Knack Story: From a Boyhood SW Receiver to the Design of the sBITX SDR

The presentation starts at about the 4 minute point. 

I think if I were only allowed to watch one YouTube video in the next year, I'd make it this one. 

In this amazing RSGB video, Ashhar Farhan VU2ESE takes us back to his earliest days as a radio amateur.  He tells us about his very early desire to build radios, his early projects, and his personal evolution as a designer and builder,  from a simple DC receiver, to the BITX, the Minima, the uBITX and now the hybrid HDR/SDR sBITX.  

There is a lot of  homebrew wisdom and tribal knowledge in this video. And we learn so many hitherto unknown details about the rigs that have become so important to us:  

-- Farhan had the EMRFD book with him on the famous flight from Sweden to India during which the BITX was designed. 

-- We learn about the origins of the BITX oscillator circuits, and that the VFO and BFO are essentially the same.  

-- I was really pleased that Farhan included a picture of my HB BITX17 rig in his presentation. 

-- Farhan discusses the difficulties he faced in obtaining needed parts in India. 

-- We actually see the nylon washers that Farhan used in the original BITX. 

-- Farhan discusses his early system for measuring coil inductance. 

-- In addition the huge contribution of EMRFD,  Farhan talks about how he was helped by Pat Hawker G3VA's writing, and the ARRL's SSB Handbook. 

-- Farhkan talks about his Tex 465 'scope and his building of a Spectrum Analyzer. 

-- We see his evolution to dual conversion. We see the conceptual birth of the Minima and the birth (thanks Wes!) of the TIA amps.  I didn't know about the HF-1.  Then Farhan designed the uBITX and now the sBITX.  

 -- Farhan talks about his practice of taking the pictures of new rigs with the new rig sitting atop the book that was most important in its design and construction.  FB. 

-- I was really blown away by Farhan's presentation of how the uBITX advertisement was inspired by and in many ways based on the Heathkit ad for an HW-101.  Amazing. 

-- I learned a lot from Farhan's discussion of SDR theory.  I pledge to spend more time with this.  I really like Farhan's hybrid HDR/SDR approach. 

-- But I have a question:  Farhan seems to say that we'd need a big expensive GOOGL computer to do the direct sampling HF SDR.  But doesn't the little RTL-SDR do just that?  Without a GOOGL?  

-- Great to see Wes's AFTIA being used in the sBITX.  

-- Really cool that Farhan has his mind on VHF transverters when designing the sBITX.   I liked use of the TCXO module to free up one of the Si5351 clock outputs.   FB.  And great to include an idea from Hans in this rig. 

Thanks very much to Farhan (who stayed up until 3 am to do this!) and to the RSGB for hosting.

Chuck Penson's Amazing New Book about Heathkit Amateur Products

 

I was very pleased to read that Chuck Penson WA7ZZE was publishing a book about Heathkit's amateur radio products.  His book is a really great guide, providing a lot of fascinating information, stuff that even those of us who have spent decades with pieces of Heath gear didn't know.  For example, I never knew that an after-market dial had been available for the HW-101.   And I didn't know that the Indian names used for many of the Heath rigs (Comanche, Apache, etc.) resulted from a suggestion from Roger Mace's wife, who was Native American. 

Chuck's book arrived just as I was putting my DX-40 novice transmitter back on the air after almost 50 years.  TRGHS.  Who knew that there were TWO versions of the DX-40?  I didn't, but Chuck did, and his book explained how to spot the difference (flashlight through the side vents -- I have the very slightly more modern version). 

When I opened the book for my first peek inside, the page opened to the QF-1 Q multiplier.  I immediately felt guilty about having brutally cannibalized several (well maybe more than several) of these things.  But right there in the text Chuck repeats my justification for the carnage:  He notes that the tuning cap has a nice 14:1 turns ratio.  Exactly.  How could I NOT pull those beautiful variable caps out of that old regen device, for re-use in superhet receivers and BITX transceivers?  

This is a wonderful book that belongs in the workshop libraries of all those who have used and loved Heathkits over the years.   

Order yours here:  

https://wa7zze.com/amateur-radio

Thanks a lot Chuck for making such a great contribution to the radio art and to ham radio literature. 

SolderSmoke Podcast #232 -- Mythbuster, Pete's Tube CW Rig, Pete's DC RX and Simple SSB Rig, NanoVNA and TinySA, Very FB Mailbag

SolderSmoke Podcast #232 is available -- Crank it in Robert!

http://soldersmoke.com/soldersmoke232.mp3

Featuring a guitar intro by Pete "Bluesman" Juliano,  playing his own composition: "Juliano Blues." 

Upcoming GQRP convention and the N6QW rig
Frank Jones and the FMLA -- Possible Victory?
IBEW Stickers:  NASA, Johns Hopkins APL....
Cycle 25 Lookin Better Today:  SFI 93   SN 47
 
Pete's Bench:
Toobular!  A Tube Transmitter
SR-160
Simple SSB rigs around the world! 
KI7NSS's Pacific 40
 
Bill's Bench
The Mythbuster and the Struggle Against the Urban Legend
W2EWL's Cheap and Easy SSB
W4IMP's IMP. Articles in ER by Jim Musgrove K5BZH and Jim Hanlon W8KGI
The Spirit of Homebrew SSB. From Electric Radio K5BZH December 1991
Reduced Front End Gain on the DIGITIA
Back on 17!  HP3SS sells HBR receiver to Joe Walsh
Maybe another Moxon?
 
SHAMELESS COMMERCE DIVISION
 
Test Gear
NanoVNA -- Alan W2AEW helped solve mystery of why NanoVNA not providing accurate readout of circuit impedance.  Over driving.  Need attenuator. 
TinySA -- Limited Resolution Bandwidth.  But you can listen with it!  See video on blog.
 
MAILBAG
-- Google Feedburner to end e-mails from the blog :-(
-- Paul VK3HN -- TIA AGC? Farhan and Paul looking into options 
-- Ciprian's Romanian Mighty Mite
-- Dino KL0S SolderSmoke GIF and graphical presentation on sideband inversion
-- Allison KB1GMX helped me on 24 volts to IRF 510 issue.
-- Dave K8WPE Wabi Sabi and Martha Stewart. And thanks for parts!  40673s!
-- Steve N8NM building a 17 meter rig with 22.1184 crystals in a SuperVXO and a 4 MHz filter.  
-- Dean KK4DAS restoring an old Zenith.  One hand behind your back OM. 
-- Pete Eaton debating SSB or DSB for 17.  Go DSB Pete!
-- Richard KN7FSZ a FB HBer.  Asked about my solid-stating of Galaxy V VFO.  
-- Walter KA4KXX on benefits of no-tune BP filters like Farhan's   FB. 
-- Jack 5B4APL on Time Crystals and Homebrewing in the 4th dimension.  FB OM!  
-- Moses K8TIY listens to the podcast with his young son Robert.  Crank it in Robert! 
-- Farhan and the SBitx on Hack-A-Day
-- Also Tom's receiver from junked satellite rig on Hack-A-Day
-- Todd K7TFC sent in beautiful message about the spirit of homebrewing. On the blog.
-- Grayson KJ7UM was on Ham Radio Workbench with George Zaf
-- AAron K5ATG running a uBitx with a  homebrew tuner and antenna.  Hope I can work him 
-- Heard Mike WA3O last night on 40 DIGITIA.  Water cooled amplifier

The SolderSmoke Team Talks to the River City Amateur Radio Communication Society (Video)

Pete and I had a great time speaking to this really nice California ham radio club (video of the event appears above).  Special thanks to club president Dr. Carol Milano, MD.  Wow, what an impressive person and ham radio operator she is:  https://www.qsl.net/kp4md/#New%20York

This club is doing a group build of a version of the famed Tuna Tin Two.    I mentioned that I had held the original TTT in my hands, and that Rex Harper had conducted a "Mojo Transfer Ceremony" that imparted TTT Mojo to my BITX17 transceiver (which was also discussed).  I promised to share the video of that momentous event.  Here it is: https://youtu.be/9RZRaFUtTcc

Thanks to Carol and the members of the RCARCS.  This was a lot of fun.  

Some Thoughts on Singly Balanced Mixers with Two Diodes and One Transformer

In 2001, out it in the Azores, I built a 17 meter version of Doug DeMaw's Double Sideband transmitter ("Go QRP with Double Sideband" CQ Magazine, February 1997).  I struggled to understand the balanced modulator -- how it mixed, balanced, and how it produced DSB.  I later presented my understanding of the circuit in my book "SolderSmoke -- Global Adventures in Wireless Electronics" pages 132-137.   In essence, I figured out that you had to think of the balancing and the mixing as two separate operations: The transformer provided the balance that eliminated the carrier (the LO signal) while the diodes presented the two signals (audio from the mic amp and LO from the VFO) with a highly non-linear path.  The LO was successively turning on both diodes then turning off both diodes. The audio signal was being "chopped" at the rate of the LO.  This produced a complex waveform that contained sum and difference frequencies -- the upper and lower sidebands.  The carrier was balanced out by the transformer because the two outputs of the transformer were always of opposite polarity, and they were joined together at the output of the mixer.    

Fast forward to 2013.  I built a 17 meter version of Farhan's famous BITX 20 rig.  Above you can see the balanced modulator stage, which also serves as the product detector. As you can see, it is essentially the same circuit as the one used by Doug DeMaw in his DSB rig. 

In 2018 I built a simple direct conversion receiver for my nephew.  For the mixer I used what I considered to be just a cut-down  version of the circuit used by DeMaw and Farhan.  I got the idea for this from Olivier F5LVG and his RX-20 receiver from SPRAT.    It had the RF signal coming in on L1 and the VFO signal coming in to the wiper of the 1 k pot.  But with this arrangement, the diodes were NOT both being turned off on half the VFO cycle, then both being turned on during the other half.  Instead, as the VFO signal swung positive, D2 would conduct and D1 would shut down.  When the VFO signal swung negative,  D1 would conduct and D2 would shut down.  It worked, but the diodes were being switched in a very different way than they had been in the DeMaw and Farhan circuits.  If you have the strong LO signal going in on L1, BOTH diodes conduct, then BOTH don't conduct.  But if you have the LO going in through the pot, one diode conducts while the other does not conduct. 

After I concluded that the BJT product detector circuit in the HA-600A was causing distorted SSB and CW reception, I tried the old DeMaw/Farhan circuit, this time in product detector mode.  See above. This worked better, but I realized that this configuration was balancing out the BFO signal, and not the IF signal.  My problem with the original product detector had been that IF signal was getting simultaneous envelope detection AND product detection.  So I decided to just switch the inputs and put the IF signal into L1 (where it would be balanced) and the BFO into  R1/R2 (the 100 ohm pot). 

This seemed like it would reduce the envelope detection problem, right?  I mean, L1 is the balanced input, right?  But I wonder if we need to consider how the diodes were being switched in this arrangement.  Instead of having both conducting and then both not conducting, in this arrangement one would be conducting during half the BFO's cycle, while the other was not.  That means that at any given moment, the two output sides of the transformer would be looking into very different loads -- hardly a condition conducive to balance. But I used LTSpice to look at the audio output under the two different port arrangements.  Sherwood advised looking at the output of the product detector with the BFO turned off --there should be no output with the BFO off.  And indeed, putting the IF signal into L1 and the BFO into the R1/R2 pot resulted in less of the distortion causing envelope detection.  The way the diodes were being switched didn't seem to adversely affect the balancing out of the IF signal.  I am not sure why this doesn't seem to cause trouble. 

There was, however, another problem with the use of this circuit in the Lafayette HA-600A:  port isolation.  The BFO signal was getting back into the IF signal input on L1.   I could see it on the S-meter.  This was worrisome not only because of the S-meter, but also because the same circuit was driving the receiver's AGC -- in effect, the BFO was turning the gain down.  Theoretically, this should not have been happening.  Look at the transformer.  the BFO currents going through L2 and L3 should be of opposite polarities and should be cancelling each other out in L1.  But obviously this was not happening.  Perhaps this was the result of the sequential way the diode are switching in this arrangement.   On the bench, if I put the BFO into L1, I saw very little BFO signal at the R1/R2 junction. If I put the BFO signal into the R1/R2 junction, I was a lot of BFO signal at the top of L1.  And that is what I saw on my S-meter when this circuit was used in the HA-600A. 

On the bench,  if I turned off the BFO and put an AM modulated signal into the junction of R1/R2, I can see audio getting through once the input signal reaches 1 volt peak.  I do NOT see that kind of "breakthrough" envelope detection when (with the BFO off) I put a modulated signal into L1.  So the singly balanced circuit is doing that it is supposed to do -- it is balancing out the the signal going into L1. 

So it seemed that with the singly balanced circuit I would have to choose: suffer from the poor port isolation or AM breakthrough.   Clearly it was time to go for a doubly balanced circuit.  And that is what I did. 

Finally, I took a look at another two diode detector, the Polyakov or "subharmonic" detector. This is a really interesting circuit that can teach us a lot about how mixers work.  Here you can run the local oscillator at 1/2 the signal frequency.  With two diodes back to back, the incoming signal is being sampled TWICE during each cycle of the local oscillator.  That is equivalent to having the signal sampled at twice the local oscillator frequency.   This circuit allows you to run the oscillator at a much lower frequency -- this could allow much greater oscillator stability.  In the circuit above, with both diodes connected, a 7 MHz incoming signal would produce a 2 kHz tone. 

Another big plus of this circuit comes if you take D1 out of the circuit (as shown).  In this configuration the circuit becomes a normal diode detector.  Here it will receive a signal at 3.5 MHz, converting that signal into a 1 kHz audio tone.  So you can get a direct conversion receiver for 40 and 80 meters fairly easily. 

Adding 10 kHz of Coverage to My BITX 17

 

Solar Cycle 25 is underway.  The Solar Flux Index and Sunspot numbers are up considerably.  I have dusted off my old BITX17 transceiver.  This time around I am using it in conjunction with a waterfall display provided online by NA5B's KiwiSDR receiver, which is located about 9 miles east of me. This SDR receiver allows me to see the entire 17 meter band.   It was this panoramic display that made me pay more attention to the fact that the Variable Crystal Oscillator (VXO) that I am using in this rig prevented me from tuning the lower 10 kHz of the 17 meter phone band (18.110 -- 18.120 MHz). 

I use two crystals switched by a relay to cover the band. One is at 23.149 MHz, the other at 23.166 MHz.  The crystal filter is at 5MHz.  With a coil and some caps I could move the frequencies of the oscillator enough to cover 18.120 to 18.168 MHz (top of the band). 

When I first built this thing, I kind of wrote off the lower 10 kHz of the phone band.  I couldn't get the oscillator to work that low, and I was already satisfied with the top 48 kHz.  But the NA5B waterfall often showed SSB stations in that lower part of the band.  I wanted to talk to them.  So I started thinking about how to do this.       

Looking at my schematic (above) I remembered that most of the frequency lowering was done by L1, a 3.2uH toroid.  I figured that to go a bit lower, I would just have to add inductance.  But I didn't want to lower the frequency provided by BOTH crystals -- I just wanted to bring the frequency with the lower crystal down a bit.  

In my junkbox I found a 1 uH coil.  I disconnected the lower lead of the 23.149 MHz crystal from its connection to the relay.  I soldered the 1 uH coil between the crystal and the relay (see picture above).  This moved the lower limit down to 18.087 MHz. 

Now crystal one provides 18.087 - 18.144 MHz 

         crystal two provides 18.137 - 18.167 MHz

So now I have the whole phone band.  Bob is my uncle. TRGHS. 

This was a very quick and satisfying little fix. As Pete says WYKSYCDS: when you know stuff you can do stuff.  Indeed.  And as I re-build and repair gear that I built years ago, I am often reminded that as time goes by, we learn more. We end up knowing more and being able to do more.   

I am also planning on rebuilding my 17 meter Moxon;  this time I will make it better and stronger.         

Using SDR without SDR Hardware -- N2CQR Adjusts Analog BITX20 using Web SDR

I know what you are thinking:  Software Defined radio with the TOTAL elimination of hardware? WHERE IS BILL AND WHAT HAVE THEY DONE WITH HIM?  

Relax my friends.  All is well at SolderSmoke's East Coast HQ.  In fact, just yesterday I was making use of one of the systems described in this video.  Here's how: 

I was on 20 meters with my BITX 20 Hardware Defined (HDR) homebrew transceiver. Everything was going smoothly.  We have some sunspots now, so DX is once again possible.  I heard a loud U.S. station (that will remain anonymous) calling CQ, so I gave him a call.  

The trouble started right after he looked at my QRZ page. You see,  I have pictures of my homebrew rigs there.  These images sometimes trigger hostile reactions, especially from guys who have almost their entire stations INSIDE their computer boxes.  I also admit to occasionally making things worse by pointing out that it is possible to build a BITX20 for about five dollars U.S.   Some guys apparently don't like hearing about this. 

Anyway, the fellow I was talking to proceeded to give me a very blunt and harsh signal report:  "Well, I suppose your signal is strong enough, but your audio is TERRIBLE!"  Interpersonal relations pointer:  This is NOT a good way to alert a fellow ham to possible technical problems in the rig that he has built by hand, from scratch, in his home workshop.  Especially when the person delivering the harsh signal report is using a "rig" that was built by credit card in a robotic factory on the other side of the planet. 

So that QSO ended rather quickly. But I did want to follow-up in the comment about the audio.  And here is where I turned to Web SDR.   Mehmet NA5B has a really nice WEB SDR receive system in Washington DC, just about 8 miles east of me.  Before 20 meters opened, I called up Mehmet's SDR on my computer, tuned it to the frequency of my transceiver and watched the screen as I asked if the frequency was in use.  I then issued a couple of hopeless CQs, again watching the screen.    I could see in NA5B's waterfall that my signal was indeed seriously lacking in low frequency audio. 

Now it was time to turn to hardware.  Rig on the bench, 'scope and sig generators fired up,   I quickly determined that the problem most likely resulted from my placement of the  carrier oscillator frequency in relation to the homebrew USB crystal filter.  I had placed it about 300 Hz too low.  This resulted in a low AF frequency roll off not at the desired 300 HZ, but instead at around 600 Hz.  That would make the audio sound "tinny." So I moved the carrier oscillator up 300 Hz and went back to Mehmet's SDR receiver.  I could see that the lows were now at the right level.  Thanks Mehmet. 

One note about the audio coming out of the many SDR radios on the air:  When you look at the passbands in the Web SDR receivers you can see audio going almost all the way down to the frequency of the suppressed carrier.  With non-SDR rigs  you usually see a gap of around  300 Hz between the carrier freq and the start of the SSB signal.  This is often the result of our filter rigs having IF filter skirts -- you would place the carrier oscillator frequency a bit down the skirt -- this would help with opposite sideband suppression and all you would be losing would be the lows below 300 cycles, which weren't really necessary anyway.  I had placed the carrier oscillator too far down on the skirt.  

Of course, sometimes SDR rigs will also have a gap between the carrier freq an the start of the audio if the operator has set the passband this way, or if the microphone attenuates below 300 Hz.  But you see a lot of signals with audio filling almost the entire passband --some of the "Enhanced SSB" guys are running audio passbands that go as low as 50 Hz.  

Has anyone else noticed this "full passband" effect when looking at the waterfalls?  
Any other tips for using Web SDR for troubleshooting?  

Quarantine Rig: VK3YE Resurrects an Old BITX Project

I think we should start calling these "Quarantine Rigs."  Many of us are pulling off the shelves rigs that we started a while back but then put aside.  Now, with the pandemic,  we have the time (and the need!) to work on them.  

I like Peter's BITX receiver video, especially the part in the beginning where he wipes the grime and oxidation off the long-neglected copper-clad board.  

Follow Peter's lead:   Pull those old projects off the shelf.  Get them going.  Now is the time.  SITS!  Melt solder and flatten the curve. 

Thanks Peter.     

Follow-Up on Scratch-built BITX17 -- Board Map and Video

In my last post I put up a time lapse GIF of my BITX 17 build from about six years ago.  Above you can see my drawing explaining what each of the stages that you see popping up on the board were.  More diagrams here: 
https://soldersmoke.blogspot.com/2013/11/bitx-build-update-19-layout-vxo-bal-mod.html
And a lot more info on this build are available on this blog.  Just use the search box for build updates (but be aware that this search will also bring up updates on later projects). 

Above is a slightly out-of-focus video tour of the board. 

I'm posting this stuff partly in reaction to the news that the BITX 40 module is no longer for sale.  I hope these posts will serve as a reminder that it is quite possible to homebrew from scratch your own BITX transceiver.  This is a fun and rewarding project.  Three cheers for Farhan! 

How A Homebrew BITX Comes Together

This is a bit of a blast from the past.  When I was building my BITX17 I paused after placing each stage on the board and took a picture.  Here is the animated GIF.  

Farhan Visits Northern Virginia and SolderSmoke HQ

 

Our good friend Farhan came to Northern Virginia last week for the 50th Anniversary Symposium of AMSAT.   We were really delighted that he also came to SolderSmoke HQ.  Elisa and I gave him a lightning tour of Washington DC (including a quick visit to The Air and Space museum) and then we headed back to the shack from some radio work. 

In the picture above you can see my BITX-20 (that Farhan designed) off his right shoulder.  Off his left shoulder you sits my ET-2 rig.  I really wanted to show Farhan how well the N0WVA regen performs -- he was impressed, especially when we started listening to SSB contacts. It was really amazing that we were doing this with just one J-310 FET.  This was great fun.  Farhan tells me that he will soon take up the "two transistor challenge."

When he was here in 2017, I tried to demonstrate my version of Rick Campbell's R2 Direct Conversion receiver.  Unfortunately, when I tried to show off the "single signal" capability that is the whole purpose for this receiver, it was NOT producing a single signal output -- you could hear the signal on both sides of zero beat.   One of the small AF chokes I had used had gone open, knocking our one of the two DC receivers.  This time I had the problem fixed and single signal reception was successfully demonstrated.  

Farhan brought me two pieces of test gear that I have needed for a long time:  A step attenuator and a two tone generator.  Paired with his Antuino, these devices will bring about a big increase in capability on my bench. 

It was really great to have Farhan in the shack.  We had a great time talking about ham radio and homebrewing.  Elisa and I both really enjoyed hearing from Farhan about his travels and about his life in India.  We are all really lucky to be in the same hobby as Ashhar Farhan. Thanks for the visit Farhan.

Here is a quick video of Farhan tuning the BITX 20.